I think a round mirror would be more visually pleasing. Maybe group the 2 blue vases? together on the same side and get something the same height for the other side

The mirror and the fireplace opening are too similar in size and shape and feel lined up. You could try turning the mirror vertically and move it over and place the lantern on the other side, with some small objects in a bit of a grouping. Try to ensure the objects are related in the style of the rustic mirror and lantern. To soften up the hearth, you could add a light colored wicker basket. houzz=];[houzz=];[houzz=]

Everything is square or rectangular. Try adding a round mirror or rounded wall art to break things up and soften the look.

When adding pieces to the mantle, go with groups of 3 in different sizes. The symmetry of those 2 blue vases is boring.

Add some greenery or tall grass in a vase at the base of the fireplace to add interest and height.

For me, the mantel is too white. It looks like you wanted to match the crown molding. Keep the mirror but move it to one side, maybe darken the frame wood colour a little and put the lantern up on the mantel on the other side. Some small picture frames 3x3 and 4x4 square, rectangular and oval in front of the mirror with photos or art in them and see if you can find one or two smaller lanterns with the same finish as what you have to make a grouping with the larger lantern on the mantel. An antique milk crate or wicker basket stuffed with blankets or even hydrangeas on the hearth would balance it out a bit better without looking too symmetrical.